Nathan,
As you well know the current rules for Modified Category do not specify a year break. The only restriction is that the car is illegal for the classic classes. Therefore, a pre-1981 car with EFI is allowed to run in the Modified Category classes.
As to my certification of a car, one would hope that all these issues are ironed out and the safety complied with prior to making a run. One of the thingsinspectors are told is that if they think there is a classification issue they should contact Steve Davies and he, along with the committee chair will resolve the problem before actual track time.
This site and the contacts in the rulebook are good sources for those new to the sport. I point most everyone I communicate with to this forum.
DW